The following formula (I) can be attributed to the alkyl diesters of saturated dicarboxylic acids obtainable according to the present invention: ##STR1## wherein R.sub.1 and R.sub.2 are each selected from the group consisting of hydrogen atoms, C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.8 aryl, alkylaryl and arylalkyl groups and R is a C.sub.1 -C.sub.8 alkyl or an alkoxyethyl --CH.sub.2 --CH.sub.2 --OR'group, wherein R' is a C.sub.1 -C.sub.6 alkyl group.
It is known to prepare (di)esters of (di)-carboxylic acids, starting from olefinic compounds, by reacting an olefin with carbon monoxide and an alcohol, in the presence of catalysts.
There are obtained the corresponding esters, diesters and betalkoxy substituted esters, of mono- and dicarboxylic acids; in the first case being unsaturated esters having one carbon atom in excess, in the two latter, being saturated esters, containing two carbon atoms in excess with respect to the starting olefin.
U.S. Pat. No. 3,397,226, for instance, describes a process in which an olefin is made to react with carbon monoxide and an alcohol in the presence of a redox-system consisting of a metal salt catalyst of the platinum group associated with a multi-valency metal salt, such as iron or copper.
Such catalysts system is kept on its higher valency or oxidation level by the addition of molecular oxygen, of halogens, or by other methods, in order to secure for the redox system its effectiveness in a continuous operation, while regenerating the redox salt species on its higher oxydation level.
The reaction, according to a preferred embodiment, is carried out in an essentially anhydrous medium, by also resorting to the use of quantitative portions of dehydrating agents, etc.
The above described redox catalytic system, in fact, is extremely sensitive to the presence of water, which leads to a reduction of the yields in the desired product with a contemporaneous increase of the formation of undesired by-products such as, for instance, CO.sub.2, etc.
Moreover, the possible dehydrating agent used therein may not be used again at the end of the reaction because it proves to be degraded. On the whole there arise, thus, considerable burdensome and expensive operational difficulties, bound to the non-selectivity of the reaction (separation of products from the mixtures obtained) and to the purification of the products that must be freed of the by-products that were formed, etc., with considerable prejudice to the economical convenience of the process itself.
Further, the use of gaseous mixes of carbon monoxide and oxygen CO+O.sub.2, involves real risks of explosion (explosion hazards), of a practically prohibitive character for a proper operation of the process.
As an alternative for the above said process, there has been suggested that the same reaction be conducted in a gaseous phase, in the presence of a catalyst of the platinum group and of an ester of a nitrous acid and possibly of oxygen.
The process, described in U.K. Pat. Application No. 2,024,821, asserts to obtain better yields and a greater selectivity. Nevertheless, also in this process, the contemporaneous quantitative forming of by-products, makes the problem of separation and purification relatively burdensome with regard to a correct evaluation of the industrial economical convenience.
On the other hand, the presence of oxygen in the cycle may lead to the formation of explosive organical nitrates.